<?php
include("conn.php");
mysql_select_db("test", $con);
  $result = mysql_query("SELECT * FROM example");
echo "<table border='1'>";
while($row = mysql_fetch_array($result))
  {
  echo "<tr>";
  echo "<td width=10%>" . $row|'subject'| . "</td>";
  echo "<td></td>";
  echo "</tr>";
  echo "<tr>";
  echo "<td></td>";
  echo "<td>" . $row|'content'| . "</td>";
  echo "<td><a href='edit.php?ID=" . $row|'id'| ."'>Edit</a></td>";
  echo "</tr>";    
  }
echo "</table>";
mysql_close($con);
?>

 UPDATE `example` SET `content`='{$your_content}' WHERE ID=..

$your_content=$_GET;

<form method="GET">
<input type="text" id="content">
</form>